The present invention relates to sound-attenuating mufflers for internal combustion engines and, more particularly, to sound-attenuating mufflers generating reduced back pressure.
Numerous muffler constructions have been proposed for the attenuation of the sound component of an exhaust gas stream from an internal combustion engine. Such mufflers are designed towards achieving appreciable sound attenuation, but without substantially increasing the back pressure on the engine, which results in power loss, reduced engine efficiency, and higher fuel consumption.
In surveying the prior art, U.S. Pat. No. 4,574,914 to Flugger teaches that although the patent art contains various muffler constructions which purport to solve the problem of sound attenuation without undesirable back pressure, in reality these various structures have substantial performance deficiencies. It is well known to provide a divergently tapered centrally located conical partition for flow of gases around the partition to effect an expansion of the gases. Typical of such structures are the devices shown in U.S. Pat. Nos. 2,071,351, 2,239,549 and 2,971,599.
Some of these patented mufflers follow such an expansion partition or cone with a contraction or concentrating partition or baffle. Typical of such devices are the mufflers shown in U.S. Pat. Nos. 1,081,348, 2,667,940, 3,029,895 and 3,029,896. These mufflers, however, do significantly increase back pressure by causing the exhaust gases to reverse the direction of their flow axially as they attempt to pass beyond the concentrating or converging baffle. This flow reversal may be effective in sound attenuation, but it has been found to increase back pressure undesirably.
Even mufflers which employ alternating divergent and then convergent partitions have suffered from undesirable bulk and/or weight, inordinate complexity, or auxiliary flow channels or openings in the partitions which defeat sound attenuation. Typical of such mufflers are the mufflers set forth in U.S. Pat. Nos. 624,062, 1,184,431, 2,325,905 and 2,485,555.
Thus, U.S. Pat. No. 4,574,914 to Flugger concludes that while the successive outward deflection and then inward convergence of gases in a muffler is broadly known in the prior art, such prior art structures typically have partitions or baffle structures which induce undesirable back pressure, contain openings or passageways which diminish the sound attenuating effectiveness of the muffler, or require excessive length, diameter and/or weight.
The inventive muffler disclosed in U.S. Pat. No. 4,574,914 to Flugger is a compact, sound-attenuating muffler for a high-performance internal combustion engine in which the muffler casing has an elongated transverse cross-section with a height dimension of only slightly larger than the height dimension of the inlet exhaust pipe and a width dimension in the range of about 2 to 41/2 times the height dimension. The muffler includes a divergently tapering planar first partition which causes gases to be expanded only in a horizontal plane toward the side walls of the muffler and further includes a second partition formed to contract or converge the gases in a horizontal plane toward a central opening. The first partition has a cup-shaped back surface so that contraction of the gases around the back side of the first partition is highly effective in attenuating sound, and both partitions are sloped in a direction toward the outlet from the muffler so as to minimize the generation of back pressure, which is not substantially greater than the back pressure in a straight pipe.
The muffler disclosed in U.S. Pat. No. 4,574,914 is designed explicitly for high-performance internal combustion engines for racing cars and the like. Although the back pressure generated by such mufflers is reported to produce a power loss of less than 2%, the sound level reduction associated with this power loss is from 130 db on the A scale to about 90 db on the A scale. A sound level of about 90 db on the A scale is completely unacceptable for common passenger vehicles and the like.
There is therefore a recognized need for, and it would be highly advantageous to have, an exhaust system providing a combination of improved sound attenuation and reduced back pressure generation, yet is simple, compact, lightweight, and easy to fabricate.